It is often desirable to know the state-of-charge (SoC) and state-of-health (SoH) of a battery. Rechargeable batteries (e.g., a storage battery, a secondary battery, etc.) are used in many applications, including starting an internal combustion engine of, for example, an automobile, vehicle, or other machinery.
The SoC indicates the charge state of a battery (or an individual battery cell, or a battery pack). The units of SoC are percentage points, where 0% is empty and 100% is full. An alternate form of representing the same measurement is the depth of discharge (DoD), which is the inverse of SoC (i.e., 0% is full and 100% is empty). SoC is normally used when discussing the current state of a battery in use, while DoD is most often seen when discussing the lifetime of the battery after repeated use.
The SoH indicates the health of the battery (or an individual battery cell, or a battery pack). Over time, a battery will age and degrade, causing a decrease in the battery's ability to hold a charge and deliver its rated current to a load. Eventually, the battery will need to be replaced—i.e., once it has degraded to the point that it can no longer effectively hold a charge. The SoH represents the condition of a battery compared to its ideal conditions and/or design specifications. Like the SoC, the units of SoH may be provided as a percentage. For example, a score of 100% indicates that the battery's conditions substantially match the battery's original manufacturing specifications.
As can be appreciated, when charging a battery, in addition to SoC, it is beneficial to determine whether the battery has a low SoH, which may indicate that the battery needs to be refurbished or replaced (i.e., a “Bad Battery”). Thus, a need exists for a system, method, and apparatus for determining and displaying, to the user, a battery's SoH and SoC while the battery is being charged (e.g., during a charging cycle). A need also exists for determining and displaying whether a battery has a SoC and/or SoH sufficient to start an engine.